This invention relates to a method of removing sulfurous acid gas from smokes discharged from a variety of combustion facilities such as generating power plants.
The disposal of toxic substances, especially sulfurous acid gas, in the smokes discharged from a variety of combustion facilities is a serious problem in the regulation of environmental pollution, and strenuous studies are being made and accessory purification facilities are being constructed at huge expenditures, by electric power companies and chemical companies.
The toxic substance removing methods presently being employed are classified broadly into a dry process using active carbon or manganese as absorbent, and a wet process using liquid slaked lime, caustic soda or aqueous ammonia as absorbent. The dry process is inferior to the wet process in respect of desulfurization ratio, the desulfurization ratio of the former being 70 - 80%, and suffers from the disadvantages that the regeneration of the manganese powder or active carbon is difficult and that the useful life of the active carbon is short or the scattering manganese powder causes the secondary environmental pollution. The wet process is advantageous in that the desulfurization ratio is higher than 90% but has the disadvantage that it lowers the smoke temperature. Further, either process involves chemically complex operations in the effective utilization of the huge amounts of by-products or in the disposal of the same in the form of non-toxic substances, and poses many problems yet to be solved when it is practiced in the actual waste flue gas treating apparatus.
In the past, the use of the dry process has been predominant in the treatment of waste flue gases for the reason that it does not lower the waste flue gas temperature and, therefore, an air pollution preventing effect can be expected by the diffusion of the gas from a chimney. However, with the amount of waste flue gas increasing more and more, the concentration of gas released in a fixed zone has increased and it appears that the effect of diffusion of the gas has reached its peak. Under such circumstances, it is the recent trend to remove the sulfurous acid gas from the smoke as much as possible. Further, in the conventional wet process the transportation of large amounts of chemical materials used as neutralizing agents and large amounts of by-products, the effective utilization of the by-products and the conversion of the by-products into non-toxic substances, have been big problems yet to be solved.